The present invention generally relates to inrush current protection circuits and more particularly, pertains to an inrush current control circuit for limiting the inrush current from a DC voltage supply to a load capacitor.
Many flight instruments and military equipment commonly employ capacitors on a power buss to filter out current spikes and noise that would otherwise be impressed on the power buss. During power-up, these capacitors initially require large amounts of current to charge up, resulting in a large inrush current drain on the power buss. This can cause disruption of other instruments and equipment connected to the power buss.
For example, aircraft that distribute DC power from a generator to on-board systems protect the generator from excessive current loading with a circuit breaker. During power-up of an on-board system, capacitors in the on-board system draw large amounts of current to charge up. If the capacitors of the on-board system attempt to draw more current from the generator than that allowed by the circuit breaker, then the circuit breaker will activate and terminate DC power to all the on-board systems connected to the generator.
Also, spacecraft in earth orbit use solar cells to provide power to internal systems. The amount of current provided by the solar cells is limited by the amount of light falling on the cells. If the capacitors of an internal system attempt to draw more current from the solar cells than they can supply, then the output voltage of the solar cells will drop sharply. The sharp drop in the output voltage can cause disruption of other systems drawing power from the solar cells.
Therefore, there is a need to protect against large current drains on a power source during system power-up and the disruption of other systems connected to the power source. Specifically, a protection circuit is needed between the power source and each system with a capacitive load drawing power from the power source to limit the inrush current during system power-up.
The inrush current control circuit of the present invention addresses the above problem by limiting the inrush current drawn from a DC power source during system power-up. An input terminal of the inrush current control circuit is connected to a DC power supply and an output terminal is connected to the load capacitor of a system. When the DC power supply applies a DC voltage to the input terminal, the inrush current control circuit of the present invention produces a voltage ramp at the load capacitor instead of an abrupt DC voltage. The voltage ramp results in a constant low level current to charge up the load capacitor compared to an abrupt DC voltage which can result in a high level current.